1. Field of the Invention
This invention relates to a data transfer system for use in, for example, a video tape recorder, which transfers data from a microcomputer incorporated in the recorder to an integrated circuit for controlling a servomotor incorporated therein.
2. Description of the Related Art
Published Unexamined Japanese Patent Application No. 57-106262 discloses two types of data transfer systems. The first type employs two transfer lines for transmitting a clock signal and a data signal, respectively. The second type is identical to the first type, except that it has one more line for controlling the start and finish of data transmission.
More specifically, the first-type system comprises a data transfer apparatus for transmitting clock signal and binary serial-data signals, a bidirectional bus having two lines connected to the data transfer apparatus, and a plurality of data transfer/receiving terminal units connected to the bus. Each of the terminal units has two terminals, one for receiving a signal from the bidirectional bus, and the other for transmitting a signal in reply to the signal received.
Since each of the data transfer/receiving terminal units requires transfer/receiving terminals connected to the bus, respectively, the system inevitably has a complex hardware structure.
Further, the data transfer apparatus transmits a data signal which has identical logic levels at times corresponding to the leading and trailing edges of a clock signal, but does not transmit a sub-data signal which has logic levels temporarily inverted at any time between the leading and trailing edges of the clock signal. With this structure, it is impossible to transmit lots of data.
On the other hand, the second-type system requires as many as three transfer lines.